Year long sabbatical - tax refund?

Ktmaria11

Hi, new to this so please bear with me.
I will be going on a year long sabbatical from 1/10/19- 30/09/20 therefore only working half of this year’s tax year (and less than 183 days). As I am not leaving my employment I will not get a P45. I have been looking at what to do and the form P85 seems the correct thing in my circumstances (will not be working whilst away and will be paying normal tax rate until end of September) as I won’t have a p45 will I be able of do this or do I have to wait until the end of the tax year to then request a refund? How will I know if I am entitled to a refund of any kind (any way I can work that out just so I know for budgeting reasons)
Thanks everyone in advance

BoGoF

Will you remain on the payroll with nil pay being put through each month? If so your employer will make any refund every month.